I remember reading them back in the early 90s (Robin Hood: Prince of Thieves, Far and Away, Back to the Future). They don’t seem to be a thing anymore (or am I just not noticing them).
As an aside I remember liking them but I was a preteen at the time so maybe they were terrible and I just liked the movies.
There are still some novelizations, as you can see in the article below, but they were much more popular before it was so easy to watch movies at home.
https://en.wikipedia.org/wiki/Novelization